New to hardness testing, any tips and tricks?

Our shop just got into doing our own hardness testing due to several parts that were rejected by our customer for being too hard or soft, we were trusting the shop who did the heat treating to do a good job. So our shop just bought a Wilson Rockwell tester along with several several different test blocks. Most of what we make that needs to be tested are pump wear rings made from spin cast CA15 or CA40 that run together were one is softer than the other one, they have to be in a 50 point range from 215/265 BHN to 375/425 BHN so we have to convert the Rockwell numbers which is not a good idea I know but we are working on getting a Brinell tester also, I've noticed that surface finish has a lot to do with the results as well as how rigid and flat the part is. Also testing on a single ring can result in 3 or 4 points difference in readings if checked at 0-90-180-270 degrees, is this a sign of bad heat treating or material that isn't blended well? I just wanted any tips that may be useful, thanks.

As you correctly stated, converting rockwell to brinell is not a good idea. That being said, alot f us have to make due with what we have these days. Ideally you should be using the same instrument that your customer has.

A couple of questions. Are you using a diamond or ball indenter, what size ball? Is your weight stack correct for the indenter? Are you getting consistent readings on you master blocks? -Mike

Make sure you have a rigid and repeatable setup.

The Brinnell ranges you're trying to test are a bit awkward. For the 400 range you probably want a diamond penetrator and Rockwell C conversions. For the 250 or so, dropping down to a 1/16" ball and Rockwell B scales might be better.

There's also a difference in testing parts that are case hardened vs. those that are through hardened. Are both parts through hardened?

Holescreek said:

As you correctly stated, converting rockwell to brinell is not a good idea. That being said, alot f us have to make due with what we have these days. Ideally you should be using the same instrument that your customer has.

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Our customer also checks with a Rockwell tester.

Holescreek said:

A couple of questions. Are you using a diamond or ball indenter, what size ball? Is your weight stack correct for the indenter? Are you getting consistent readings on you master blocks? -Mike

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Weight stack is correct as far as I know, we use 2 add-on weights for the
"C" scale and 1 for the "B". Currently have a ball indenter, one for the "B" scale and one for the "C" scale, and we are getting +/- .5 point on the test blocks we have.

PeteM said:

The Brinnell ranges you're trying to test are a bit awkward. For the 400 range you probably want a diamond penetrator and Rockwell C conversions. For the 250 or so, dropping down to a 1/16" ball and Rockwell B scales might be better.

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For the softer rings we are using the "B" scale, some go over that so we switch to the "C" scale for them.

PeteM said:

There's also a difference in testing parts that are case hardened vs. those that are through hardened. Are both parts through hardened?

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Both parts are hardened through, we send out one long pre-roughed tube of material and then make and part-off the rings, then test each one on the parted off side, it's usually very smooth, if not we face it smooth with light feed so no feed lines to mess up the testing.

Are the parts ground parallel prior to testing or are you testing right out of the heat treating process?

Oops, didn't read the entire post I guess. Anyway, try grinding parallel(light cuts) and see if you get more uniform results.